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My dad owns a really neat star trek Christmas tree ornament that plugs into a standard bulb socket in a Christmas tree light string. It has a button that, when pushed, causes Spock to say a brief holiday message.

I want to know where I should start to be able to create my own ornament like this. I know you can get programmable chips that can play a sound clip when hooked up to a speaker, and it can be powered from a tiny battery. But that is DC, whereas light strings are AC.

Can someone give me an idea of a simple way to run something like that off of the Christmas tree light strands?

Stephen S
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  • Probably the easiest and cheapest way to do it is to buy a recordable greeting card and recycle the guts of the card into your ornament. It will come with a battery, so you don't need to worry about powering it from the light string. – Johnny Sep 05 '13 at 21:59
  • If you really want to do this, you have to figure out the voltage and current ratings available. Mind you that many light strings are not galvanic isolated from the mains, therefore isolation is a top priority. Another thing to keep in mind is if you interrupt the loop, the voltage across it will rise to the full mains voltage which may easily blow electronics when not designed for that situation. – jippie Sep 06 '13 at 05:32

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This is less of an answer than it is helpful information. Newer versions of these have long since moved to battery power and don't stay lit.

Small AC Incandescent Christmas Light Bulb strings are typically 100 bulbs, set up as two sets of 50 in-series bulb strings in parallel. (The C6 bulbs are 15v and C7/C9 bulbs are typically 120v and all wired in parallel)

With a typical 120v line, that means each bulb in a 50 bulb set is 120 / 50 = 2.4v AC, but there is variations where there are more or less bulbs in each set.

I was only able to find these two pictures of the inside, which makes it very hard to figure out the circuit, but it helps. Notice the connector is just two wires.

enter image description here enter image description here

Some of the parts are obvious. There seems to be a shunt, a miniature light bulb between where the two wires go on the pcb. This could be a shunt incase the AC bridge fails, or it could be the bulb that lights up the whole ornament. Or both. The bulb is probably in parallel with the AC bridge.

A Typical 4 diode Full Wave AC Diode Bridge/Rectifier. A Large capacitor. Most likely a standard rectifier circuit:
enter image description here

The transistor is most likely a simple amplifier for the speaker. There seems to be two more diodes, some setting resistors, and my best bet there is just a COB (Chip on board/blob) underneath, as these would likely pre-date widespread smd parts usage.

Without a good picture of the bottom, it's hard to confirm any of this, but it's a start. Additionally, I am not sure how a diode bridge in series would affect a reduced AC voltage line (I stay away from AC circuits). But this should be 2.5v DC after the rectifier circuit with the Large cap to smooth out the dc waveform. Plenty of voltage for any typical sound card circuit.

If you could take the existing one apart and take pictures, that would help us help you alot. But it seems these are held together by glue, so that would mean sacrificing it.

This page is where I found the pictures. The last update on their modding project was recent (August), so if you ask there if he could take a good picture or three of the bottom of the board, maybe they would help out.

Passerby
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You could use a bridge rectifier. it converts AC into DC by the use of one way diodes. Then use something that drops down the voltage.

LondonUnderground
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  • Assuming the AC voltage source is straight from the wall, it would probably be a good idea to precede this with a transformer to handle the voltage drop. – Nick Williams Sep 06 '13 at 00:46